Method and apparatus for frequency changing



Jan. 16, 1945. F. c. P. HENR'OTEAU METHOD AND APPARATUS FOR FREQUENCY CHANGING Filed Feb. 10, 1942 TRANSMITTER TRANSMITTER TRANSMITTER TRANSMITTER TRANSMITTER TRANSMITTER TFLIrv TRANSMITTER TRANSMIT ER TRANSMITTE Patented Jan. 16, 1945 METHOD AND APPARATUS FOR FREQUENCY CHANGING Francois Charles Pierre Henroteau, Ottawa,

' Ontario, Canada Application February 10, 1942, Serial No. 430531 In Belgium January 20, 1938 3 Claims.

This invention relates .to a method and appa ratus for frequency changing.

Methods and apparatus previously suggested for this purpose have suffered from various disadvantages. Some have been based on the operation of mechanical parts, such as commutators, and have thus been limited to work at relatively low frequencies besides being subject to the inherent limitations caused by mechanical inertia. The use of inertialess electron beams instead of mechanical commutators has been suggested, but the proposed arrangement was such that signals of adequate strength at the changed frequency would not be obtained.

It is the object of the present invention to avoid these disadvantages of prior proposals and produce a system which is not subject to the limitations imposed by mechanical inertia and at the same time is capable of producing signals of entirely satisfactory strength.

The method of the invention comprises causing a mosaic capable of electron emission to be scanned by an electron releasing beam, which is modulated by the signal and forms a record ofv the signal on the mosaic. and causing the record on the mosaic to be scanned, at a speed different from the speed of scanning by the first mentioned beam, by a beam of electrons having energy releasing power substantially greater than that of the first mentioned beam. The first mentioned beam is preferably a beam of electronsand the greater energy releasing power of the second mentioned beam in that case results from the electrons of the second beam having an acceleration substantially greater than that of the electrons of the first mentioned beam.

More specifically, the method of the invention comprises modulating an electronreleasing beam in accordance with a signal, causing the modulated beam to scan a surface capable of electron emission, projecting the electrons emitted from such surface on a mosaic capable of electron emission and scanning the mosaic at a speed different from that at which the surf-ace was scanned. The term mosaic meaning here and elsewhere in this specification a' multitude of mutually insulated tiny conducting elements, as used in many systems of television; and scanning as likewise used herein is intended to mean that electrons from a single source are directed at a number of different points on some other element successively.

When the mosaic is scanned at a. higher speed than that at which the surface was scanned, the method may be used to permit the transmission of a number of contemporaneous messages (this term to be understood in a general sense as including any intelligence or any portion of any intelligence, such as sound or pictures or writing, which may be represented by electrical vibrations) through a single transmission channel by condensing them i duration during transmission. For this purpose, each of a number of electron releasing beams is modulated in accordance with a different message, the modulated beams are caused to scan simultaneously different areas of the surface capable of electron emission, the electrons emitted from each different area of such surface are projected on a different area of the mosaic, and the whole of the latter is scanned in a time at the most equal to the time occupied in the scanning of an area of the surface capable of electron emission. When, on the other hand, the mosaic is scanned at a lower speed than that at which the surface was scanned, then the method may be used for transmitting messages by wireless in such a way as to render possible reduction of the frequency band width in transmission particularly of pictures, or the reduction of static noises in the reproduction of such messages at a receiver. In this case, one

, electron beam is modulated in accordance with the message to be transmitted and is caused to scan the whole of the surface capable of electron emission, while different equal sized areas of the mosaic are scanned simultaneously at a sub-multiple of the speed of scanning of the surface at the most equal to the number of such areas, and the signals resulting from the scanning of each such area are collected.

Apparatus for carrying out the method of the invention may comprise an envelope containing a member capable of electron emission and a mosaic also capable of electron emission, means for causing each of a number of different areas of one of the elements (i. e., the member or the mosaic) contained in the cell to be scanned by a different electron releasing beam, and means for causing the whole of the other such element to be scanned by one electron releasing beam.

The apparatus may be constructed with the member capable of electron emission and the mosaic spaced apart, with the surfaces thereof which are scanned facing each other. In this case it is desirable to provide an accelerating anode between the member and the mosaic and an electronic lens, for example, a condensing coil surrounding the anode, to focus on the mosaic electrons emitted from the member capable of electron emission. On the other hand, the latter member may be disposed immediately adjacent to the mosaic, preferably in the form of a grid the bars of which extend in the direction in which scanning is eilected, the electron releasing beam or beams intended for the scanning of the grid being arranged to strike it at such an angle that no such beam can strike the mosaic.

The invention will be more fully described in connection with the attached drawing in which Figure 1 shows one form of the apparatus with the mosaic adapted to be scanned by one electron releasing beam.

figure 2 shows the same form with the mosaic adapted to be scanned by a number of such centrating coil I5.

Figure 4 is an enlarged detailed cross section of a part of the construction shown in Figure 3.

Inthe form of construction .shown in Figs. 1 and 2, the apparatus comprises an envelope I containing a plate 2 capable of electron emission and a mosaic 3 also capable of electron emission and mounted on an insulating plate- 4 backed by a conducting signal plate 5 connected to a transmitter. Associated with the plate 2 are a number of conventionally indicated electron guns I each mounted in a separate pocket 6 formed in the end of the cell nearest to the plate. Cooperating with each gun is a modulating electrode l0 and the usual pairs of deflecting plates II and 12. At the opposite end 0! the envelope associated with the mosaic 3 is an electron gun I 3 with which cooperate pairs of deflecting plates 8 and 9. Between the member 2 and the mosaic 3 and surrounding the path of electrons passing from one of these elements to the other is an accelerating anode I4 inside the cell. Surrounding this anode on the outside of the envelope is an electronic lens in the form of a condensing coil l5 acting to focus on the mosaic 3 electrons emitted from the plate 2.

The construction of Fig. 2 is substantially the reverse of that oi! Fig. 1. In Fig. 2 one electron gun 1a, with which cooperates a modulating electrode ion is associated with the plate 2,

while a number of electron guns l3a are associated with the mosaic 3. The mosaic 3 instead of bieing backed by a single signal plate is backed by a number of signal plates l6, each of which is behind an area of the mosaic adapted to be scanned by one electron releasing beam I and each of which is connected to a separate transmitter.

In the operation of the apparatus of Fig. 1 for the purpose of enabling the transmission of a number of contemporaneous messages through a single transmission channel, each modulating electrode I0 is supplied with electrical oscillations corresponding to a different message so that the beam produced by each gun I is modulated in accordance with a diilerent message. The deflecting potentials applied to the diflerent pairs of plates H and I2 are such as to cause each beam to scan an area of the plate 2 extending over the full width of the plate but only over a. fraction of its height, as is clear from the dotted lines in the drawing. The deflecting plates I2 may in fact be omitted if desired, in which case each beam scans the plate only along a horizontal line, the thickness of which is determined by the cross section of the beam.

When a beam strikes the plate 2 it causes an emission oi. electrons proportional to its intensity .at that moment, this emission being helped it desired by connection of the plate 2 to any appropriate source oi. potential. The emitted electrons are drawn by the anode H towards the mosaic 3 and focused on it by the con- In this way. series of electrostatie charges representing different messages are produced on diflerent areas 01' the mosaic 3 corresponding respectively to areas or the member 2 scanned by different beams. The whole mosaic and thus these areas in successsion are scanned, in a time at the most equal to that occupied in the scanning of one area of the plate 2, by an electron releasing beam produced by the electron gun I3, and a series of corresponding signals is thus sent to the transmitter in the manner well known. Thus, in the example illustrated, scanning oi! the mosaic is eflected five times as fast as scanning on the plate 2. 0bviously, the signals transmitted in one scanning period will generally represent only a small fraction of, say, the full conversations constituting the messages applied to the electrodes [0.

In the operation of the apparatus of Fig. 2 in the transmission of messages by wireless in such a way as to render possible 'the reduction of static noises in the reproduction of these messages at a receiver, the electrode Illa is supplied with oscillations corresponding to the message to be transmitted and the beam from the gun 1a is thus modulated accordingly. The modulated beam is caused to scan the whole of the plate 2, and electrons emitted from this plate are, as in Fig. 1, caused to strike the mosaic 3 at positions corresponding to those from which they were emitted from the plate. Different areas 01' the mosaic, each backed by a separate signal plate l6 connected to a separate transmitter, are scanned by electron releasing beams from different electron guns l3a in a time at the most equal to that occupied for the scanning of the whole of the plate 2. Thus, the one-fifth, with the apparatus shown-0t the message applied to the modulating electrode Illa during one scanning of the plate 10 are transmitted in a time equal to the actual duration of the whole of that message, so that their frequency is correspondingl reduced.

Reception of a number of contemporaneous messages sent through the same transmission channel with apparatus of Fig. 1, is effected with the apparatus of Fig. 2'. The incom'ng signal, carrying in succession fragments of different messages, is applied to the modulating electrode Illa, and the signal plates 16 are connected -to receivers for the several individual messages.

Reception of a message transmitted with the help of the apparatus of Fig. 2, is efiected with the apparatus of Fig. 1. The incoming signals, each carrying low frequency fragments of the message are applied to the control electrodes l0, and the message is reconstituted at its original frequency by the rapid scanning of the mosaic 3.

When the apparatus of Fig. 1 or Fig. 2 is used for transmission and that of the other figure for reception, the number of signal plates l6 and electron guns [3a must, of course, correspond to the number of electron guns I, and the scanning by the plates II and I! must be synchronized with that by the plates 8a and 9a, while'that by the plates 8 and 9 must be synchronized with that by the plates Ho and In.

In Figures 3 and 4 a modification of the apparatus of the invention is illustrated. In this modification the member capable of electron emission is disposed immediately adjacent to the mosaic 3 rather than some distance away from and facing it as in Figs. 1 and 2. Instead of being in form of a plate, the member is in the form of a grid H, the bars I8 of which extend substantially parallel to the lines along which it is scanned (i. e. horizontally as shown in Fig. 3). The electron gun 1a is in such a position and directs its beam at such an angle that, as shown in Fig. 4, the beam effectively scans the grid, but the latter forms a screen to prevent the beam from striking the mosaic 3 The electron guns I3a of which there may, of course, be more than the three shown, instead of being disposed at an angle to the mosaic as in Fig. 2 are arranged in the side of the envelope opposite to it so that the beams which they produce can reach the mosaic directly between the bars of the grid. An electrode is may be used in certain circumstances to aid in controlling the movements of the electrons emitted by the electron releasing beams.

The operation of the device shown in Figs. 3 and 4 is basically the same as that of the devices of Figs. 1 and 2. Electrons emitted from the grid I! under the influence of the electron releasing beam from the electron gun 1a are attracted to the closely adjacent mosaic. Different areas of the latter are scanned by beams from difierent electron guns l3a, andthe electrons thus emitted are collected by the electrode 19.

Although a device of the kind shown in Fig. 3 but with one electron gun associated with the mosaic and a number of electron guns associated with the grid has not been shown, it will be obvious that one of this kind could easily be constructed.

In all cases the scanning of the plate 2 or gri H; as the case may be, and of the mosaic 3 may be continuous. However, it may be in some cases found desirable to scan these elements alternately. In this case two identical devices could be connected somewhat in the manner shown in my application, Serial No. 189,688, filed February 9, 1938. Such an arrangement might be particularly desirable in the case of the device shown in Fig. 3, since if scanning of the two elements were efiected alternately, the potential of the electrode l9 could be made more positive during scanning of the mosaic than during scanning of the grid. Without this, there might be some distortion in the use of the device as a result of electrons emitted from one element of the mosaic returning to another instead of going to the electrode IS, the potential of which could not be made too positive without attracting to it electrons emitted from the grid which should have gone to the mosaic.

The invention is not intended to be limited to the devices specifically described and illustrated, since they could be modified in many ways. For instance, both the plate or grid and the elements of the mosaic might have coatings of photoelectric material, and light beams be usedinstead of electron beams. Again the areas of the plate 2 or the grid scanned by beams from the electron guns 1 need not all be of equal size. For example, if the apparatus were used for the transmission of pictures and sound over the same circuit in television, the area covered by the I beam modulated by picture currents might be,

say, ten or more times that covered by the sound current modulated beam. The result of this would simply be that the frequency of transmissionof the picture curzyits would be negligibly increased while that of thetransmission of the sound currents would be very greatly increased.

This application is a continuation in part of my application, Serial No. 252,030, filed January 20, 1939, now Patent No. 2,277,516.

What I claim as my invention is:

1. The method of changing the frequency of a signal in apparatus including a mosaic capable of electron emission, an electron releasing beam modulated by the signal, and a beam of electrons having energy releasing power substantially greater than that of the electron releasing beam, which comprises scanning said mosaic with said modulated electron releasing beam to form a record of said signal on said mosaic, and scanning the record on said mosaic with said beam of electrons at a speed diflferent than that of the scanning with said electron releasing beam.

2. The methodof changing the frequency of a signal in structure including a surface capable of electron emission, a first electron releasing beam, a mosaic capable of electron emission, and a second electron releasing beam, which comprises modulating said first releasing beam by the signal, scanning said surface with said modulated beam, projecting the electrons emitted from said surface on to said mosaic, and scanning said mosaic'with said second electron releasing beam at a speed different from that at which said surface was scanned.

3. The method of transmitting a number of contemporaneous messages through a single transmission channel by condensing them in duration during transmission in apparatus including a plurality of electron releasing beams, a surface capable of electron emission, a mosaic capable -of electron emission, and a further electron releasing beam, which comprises modulating each of said plurality of electron releasing beams with a different message, scanning simultaneously difierent areas of said surface with said modulated beams, projecting the electrons emitted from each different area of said surface on a difierent area of said mosaic, and scanning the entire mosaic with said further beam in a time at the most equal to the time occupied in the scanning of an area of said surface. FRANCOIS CHARLES PIERRE HENROTEAU. 

